It is well known that the productive capacity of a multiple wire-rod rolling mill train is mainly determined by four factors; it depends on the base cross section of the billet within the roughing line, on the length of the billets entering the roughing line, on the number of rolling lines, and finally on the rod delivery speed.
Practical experience, however, has indicated that certain problems are encountered with all these factors during the operation of a continuous rod mill. The base cross-section of the billets on a multi-pass rod train are subject to the so-called Konti law and cannot be made of unlimited size, because each enlargement of the billet also requires an increase in number and a reduced billet entrance speed into the pre-roll line. For that reason not only is the passing time of the billet through the entire rolling train extended (which has an unfavorable influence on the heat balance) but lowering the entrance speed into the pre-roll line under 0.07 m/sec. presents the additional danger of creating heat cracks on the rolls.
The length of the rolled billets may theoretically be of any dimension, because billets from a given base cross section may as a practical matter be welded to any length. This type of operation, however, is not practical when a multi-wire rod train is to be used.
The delivery speed can theoretically be increased. Practically, however, there are limits, because the necessary auxiliary equipment such as shears, reels, etc. at the end of the train can operate safely (in the present state of the art) only up to maximum output speed of 60 m/sec.
Finally, the number of rolling lines cannot be chosen arbitrarily based on the machinery available; the limit with today's state of development lies in a four-line train.
There have been made several attempts to operate multi-line trains to obtain high production capacity and large bundle weights. For example, in German patent DT-OS No. 1,527,694 a continuous light-section steel train was revealed and has, following a furnace, a roughing train, intermediate train, and finish train, wherein the rough train and/or the intermediate train each have a single rolling line operation, but the finish train is arranged for multi-strand rolling operation and wherein each line has an added special bundle storage. The bundle storage is interchangeably supplied from the intermediate train with a rod line and is designed as after-furnace or equalization-furnace. In that way the roughing train and the intermediate train can be driven independently of the rolling speed of the finish train and the bundle storage acts as a buffer for the finish train. The base cross section of the billet entering the roughing train can thereby be enlarged without the entrance speed into the roughing train being lowered below the critical speed of 0.07 m/sec., because of the fact that the after-furnace or equalization-furnace operates as a buffer, so that the so-called Konti law is not operative.
A multi-strand roll train which is similar with respect to the after- or equalization-furnaces, but somewhat modified, has been taught by German patent DT-AS No. 1,808,822. In the arrangement shown in that patent the after- or equalization-furnace is positioned between the roughing train and the intermediate train, so that, instead of a bundle storage, a roll-through storage is provided. The multi-strand line operation also begins here in the intermediate train of the mill.
In spite of the fact that these known, continuous multi-strand trains provide an intermediate storage by the provision of the after- or equalization-furnace located in an area between one or the other successive rolling lines allow the so-called Konti law to be inoperative and thereby the possibility is presented of introducing billets into the roughing train with a base cross section of approximately 180 mm with an entrance speed of at least 0.07 m/sec., nevertheless, considerable disadvantage is still present with these known designs. Since obviously the achieveable pass reduction within the individual roller stands is limited, practically every increase of the base bar cross section requires a certain increase in the number of stands, at least within the roughing train. In case one achieves a high production capacity with large bundle weights by replacing the standard billet cross section of 100 mm with an enlarged billet cross section of 180 mm, then the plant investment for the roughing train line is more than doubled. Because of the increase in the number of stands, an extension of the roughing train is necessary, and, consequently, a longer shop for the housing of the machinery is also required. Additionally, the after- or equalization-furnaces (which serve as intermediate storage) have to be introduced into the mill to guarantee constant temperatures of the rod stock during intermediate storage; this introduction also increases still further the total expenditure because of the corresponding necessary increase of the length of the shop.
The design of the intermediate storage as after- or equalization-furnace has, in addition to the increased energy expenditure, the disadvantage that the after-heating of the rod leads to the danger of scale formation. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, the object of the present invention not only to eliminate all the disadvantages previously described in continuous multi-strand rod rolling mills, but also make it possible to use billets of large base cross section for achieving high production output and larger bundle weights.
Another object of this invention is to create a multi-strand rod rolling mill with high production capacity to produce large bundle weights, the mill having a furnace after which is provided a roughing train and a separate intermediate and finish train for each individual rod rolling line and using intermediate and finish train as used in rolling with the classic billet cross section of, for example, 100 mm and capable within the roughing train of rolling large billet cross sections up to 200 mm with a minimum number of stands without the entrance speed of the billets going below the critical speed of 0.07 m/sec. and without an increase in billet residence time in the roughing train, which increase could endanger the entire heat balance in the rod rolling mill.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.